Lithium ion batteries are the key technology for the majority of rechargeable battery systems in portable electronics and for e-mobility. Most of today's applications of lithium ion batteries face growing demands for significantly improved performance: higher energy density, improved cycling performance, safety, flexibility in device integration, and so forth.
As to what concerns anode materials for lithium ion batteries, a clear challenge is to implement an alternative to graphite, which is presently dominating the market of lithium ion batteries. Graphite based anodes provide for a theoretical gravimetric capacity of 372 mA h g−1 by forming LiC6. The most promising near-future, high-capacity alternatives or useful additives to carbon are those based on tin (Sn) and silicon (Si), and some other elements that can form alloys with lithium, all having significantly higher theoretical specific capacities than carbon. In particular, the gravimetric capacity of fully lithiated tin (992 mA h g−1 for Li4.4Sn) is more than twice as high as that of graphite, when the volumetric capacity is higher by at least one order of magnitude. Other commonly discussed advantages of metallic tin are the following. Firstly, tin has a higher operating potential when used as anode, making it less reactive towards electrolytes and, therefore, much safer. Furthermore, unlike graphite, it does not undergo irreversible capacity losses due to solvent intercalation. Moreover, tin is highly abundant, inexpensive and environmentally benign.
The major issue with alloy anodes is their severe capacity fade arising from a huge volume change up to 300% occurring during a charge-discharge process, i.e. during alloying-dealloying. This volume change leads to lattice stress and consequential cracking and crumbling of the alloy particles during cycling, resulting in abrupt loss in capacity within a few charge-discharge cycles. To overcome the above problem, various strategies have been proposed and tested. For example, Sony Corporation has introduced a new lithium ion battery called Nexelion® having an amorphous Sn—Co—C composite as the anode material.
A different approach relies on reducing the size of individual grains in the anode material. US 2007/0020519 A1 (Kim et al.) discloses an anode active material for a lithium ion battery, the material comprising a tin-based nanopowder that is capped with a triazine based monomer. The tin-based nanopowder is reported to have a particle size form about 10 to about 300 nm. Similarly, U.S. Pat. No. 8,192,866 B2 discloses a tin-based anode material containing capped tin nanoparticles.